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tcp: Revert "tcp: remove header prediction"

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This reverts commit 45f119bf93.

Eric Dumazet says:
  We found at Google a significant regression caused by
  45f119bf93 tcp: remove header prediction

  In typical RPC  (TCP_RR), when a TCP socket receives data, we now call
  tcp_ack() while we used to not call it.

  This touches enough cache lines to cause a slowdown.

so problem does not seem to be HP removal itself but the tcp_ack()
call.  Therefore, it might be possible to remove HP after all, provided
one finds a way to elide tcp_ack for most cases.

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal
2017-08-30 19:24:58 +02:00
committed by David S. Miller
parent c1d2b4c3e2
commit 31770e34e4
8 changed files with 223 additions and 6 deletions
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4
net/ipv4/tcp.c
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@@ -1963,8 +1963,10 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
tcp_rcv_space_adjust(sk);
skip_copy:
if (tp->urg_data && after(tp->copied_seq, tp->urg_seq))
if (tp->urg_data && after(tp->copied_seq, tp->urg_seq)) {
tp->urg_data = 0;
tcp_fast_path_check(sk);
}
if (used + offset < skb->len)
continue;